1. Technical Field
The present invention relates generally to a metal surface modification apparatus for modifying metal surfaces by radiating electron beams onto the metal surfaces, and more particularly to a metal surface modification apparatus for modifying the surfaces of titanium implants made of a titanium alloy.
2. Description of the Related Art
Titanium is a light metal having a specific density of 4.5, and is relatively lightweight. In particular, titanium is a stable metal having high corrosion resistance. Titanium is not easily dissolved in the human body due to its difficulty in reacting with a biological material. Furthermore, the amount of titanium absorbed into the human body is extremely small because it is not an essential biological element, and titanium has low toxicity. Accordingly, titanium and titanium alloys are widely used as materials for medical appliances. Examples of biocompatible titanium alloys include: TiNi, Ti-6Al-4V, Ti-6Al-7Nb, and Ti—Nb—Sn. Although titanium usually contains a predetermined or less quantity of impurities, both titanium and a titanium alloy will be simply referred to as “titanium” in the following description.
Titanium is, however, corroded by fluoride. When titanium is used as a material for dental implants, there is the concern that titanium may be absorbed into the human body because toothpaste contains fluoride. Although titanium is known as having extremely low toxicity, titanium implants are generally subjected to surface treatment for the formation of a coating in order to further improve corrosion resistance. For this reason, titanium is still suitable for a material of dental implants that require high corrosion resistance and high abrasion resistance.
Processes for treating the surface of a titanium implant may be mainly classified into a process of treating the surface of a titanium implant in an aqueous solution, and a process of treating the surface of a titanium implant in a vacuum or air. The process of treating the surface of a titanium implant in an aqueous solution has advantages in that required equipment has a relatively simple configuration and it is possible to treat the surface of an implant having a complex shape. In contrast, the process of treating the surface of a titanium implant in a vacuum or air has advantages in that it is possible to perform surface treatment without using chemical agents and it is possible to form a thinner coating.
In the case of the process of performing surface treatment in an aqueous solution, there is a case where chemical agents used in the process remain on an implant, and thus there is a need to consider that there is the concern that chemical agents are gradually dissolved in the human body during long-team use. Furthermore, in order to make the surface of a molded titanium product smooth like the surface of a mirror, it is required to mechanically polish the surface to a certain finished surface roughness. As the thickness of a coating obtained by the surface treatment becomes thinner, a rough surface caused by mechanical processing is more likely to remain on the surface of an implant after surface treatment. For this reason, a treated person is likely to feel pain.
Examples of a process of modifying the surface of a titanium artificial tooth or implant by using electron beams are disclosed, for example, in patent documents 1 to 3. The surface modification process using electron beams does not use chemical agents. Furthermore, the surface modification process using electron beams is designed to convert the surface layer of a metal into a microcrystalline structure by using a physical principle, and can provide a thin modified layer having higher corrosion resistance, higher abrasion resistance and higher endurance than a coating layer. Moreover, this process has an advantage of obtaining a smooth surface, which cannot be obtained by mechanical processing. In particular, when electron beams having low-density energy are radiated onto a relatively large area, it is possible to obtain an extremely thin modified layer with less non-uniform irradiation.